I often see projects in which designers thoughtlessly terminate round bars with 135° hooks of at least 10Φ length. But is such a solution always sufficient?
This is probably the case for beams without substantial torsional moments, but the situation is quite different in columns. In the corners of columns, the longitudinal bars are often significantly compressed, making using 135° hooks difficult or impossible.
At MR Statik Gruppe, we have introduced the principle of using straight hooks when there is more than one longitudinal bar in a corner or when the diameter of the main reinforcement is more than Φ≥25 mm.
The specifications of the DIN EN 1992-1-1 standard should also be noted. According to this standard, hooks bent at 90° with 15 reinforcement diameters must be used for structures with a required fire resistance of R≥90. In extreme situations, these additional centimeters can significantly affect the stability of the structure, especially under fire conditions.
